Aircraft typically include a variety of air measurement devices and air data sensors for measuring various parameters associated with air flow. For example, air data sensors may measure airspeed, air pressure, altitude, air temperature as well as local air flow angles as the aircraft disturbs the air that it flies through. Measured flow angles may include angle of attack and angle of sideslip.
Air data sensors such as alpha vanes and beta vanes are commonly used for measuring local flow angles such as angle of attack and angle of sideslip. Resembling small weather vanes having a pivot arm that pivots into the airflow, alpha and beta vanes are mounted on strategic areas of the aircraft such as on a boom extending outwardly from a wing leading edge or nose of the aircraft. Alpha and beta vanes may be coupled to a potentiometer or other device which generates an electrical signal that varies in proportion to angular displacement of the alpha or beta vane in response to local flow about the aircraft.
Accurate measurements of angle of attack and angle of sideslip are necessary for safe operation of the aircraft as such air data is provided to flight control computers to facilitate control of the aircraft. In this regard, air data sensors must be calibrated such that the true angle of attack and true angle of sideslip of the aircraft can be provided to flight instrumentation and flight computers.
Conventional methods for calibrating air data sensors include leveling fixtures and tooling which, although satisfactory for their intended purposes, possess certain drawbacks which detract from their overall utility. For example, conventional leveling fixtures and tooling are typically adapted to fit specific types of air data sensors and may be unique to each vehicle and location. Such fixtures and tooling must be temporarily installed on the alpha or beta vanes or the fixtures may be mounted on the air data boom in a time-consuming process. After mounting of the tooling and/or fixtures, calibration operations are performed and the fixtures and tooling must then be removed and stored for later use.
A further drawback associated with conventional calibration methods is the amount of time required for calibrating each air data sensor. Such fixtures and tooling must be carefully installed and checked for alignment with a desired axis of the aircraft so that the flight instrumentation may receive accurate information regarding the true air flow parameters.
Another drawback associated with conventional fixtures for calibrating air data sensors is related to the limited accuracy of such fixtures. For example, one commercially-available calibration fixture comprises a visual scale that is mounted directly on the air data boom and is aligned with a fin on the pivot arm to allow calibration of the alpha or beta vane. Unfortunately, due to the relatively short length of the pivot arm of the air data sensor, the accuracy of calibration is limited. As a result, the accuracy with which a directional air data sensor measures air flow direction may result in the delivery of inaccurate data.